Synchronicity of Sexual Tides w Moon Tides

{EXCERPTS FROM Women, Orangutans and the Moon Coloring & {NOTES} Added}

Tina Proctor
14 August 2005

Women, Orangutans and the Moon


Nothing could have surprised me more when I began my menstrual flow at the dark of the moon in October, 2004. I am post-menopausal and haven’t bled for 2½ years. Why did this happen? … Could my own focus on menstruation actually bring on a period after such a time? Perhaps it was because we were two weeks away from a total lunar eclipse and I was feeling the lure of the mistress of tides.
The paper reflects on the physical and cultural connection between human menstruation and the moon and questions what effect the moon might have on orangutan biology and cultural development.

Traditionally the length of a woman’s menstrual cycle has been defined as 28 days or the length of the lunar cycle. Lunar cycles are actually 29.5 days and studies have shown that a woman’s cycle may normally be anywhere between 23 and 35 days, the average being described as 29.1 days [4] to 29.5 days. [5]
Shuttle and Redgrove cite the research of Walter and Abraham Menaker [6] who compare the mean length of the menstrual cycle at 29.5 days with the length of the synodic lunar month[7] of 29.5 days. They show that the mean duration of pregnancy from last menses is precisely 9.5 lunar months. In going back to conception, the mean duration of pregnancy is nine lunar months; therefore, it is likely that a child conceived on a given day of the lunar month would be born on a corresponding day nine months later. The Menakers counted more than 120,000 births in a New York City hospital during 13 lunar months and found that fewer births occurred on the day of the new moon than on any other day. This is what would be expected if more women tend to have their periods at this time than any other. Full moon days, however, had more births, which is also what you would expect if people tended to ovulate on the full moon.

{“The sidereal month is the time the Moon takes to complete one full revolution around the Earth with respect to the background stars. However, because the Earth is constantly moving along its orbit about the Sun, the Moon must travel slightly more than 360° to get from one new moon to the next. Thus, the synodic month, or lunar month, is longer than the sidereal month. A sidereal month lasts 27.322 days, while a synodic month lasts 29.531 days.

The Menakers did two other studies at private hospitals, each looking at 250,000 pregnant women. Once again, the new moon was associated with fewer births and the full moon with an increase of them. They found that births on day fourteen, the full moon, when the Menakers postulated the likelihood of ovulation occurring, deviated “to an extraordinary extent above the mean.”[8] They concluded that there is a small but statistically significant synodic lunar influence on the human birth-rate, and presumably on the conception rate and the ovulation rate.

{Menakers 1959, “most auspicious time seems to be a day before full moon…and also full-moon day (but not the day after full moon).” –American Journal of Obstetrics & Gynecology}

…  McClintock studied 135 women in her dorm during her senior year, found statistical evidence of menstrual synchrony and published the results in the prestigious journal, Nature in 1973.[9] McClintock postulated that human pheromones were the cause of the menstrual synchronization found with women who live together.

Winifred Cutler, at Wayne State University, studied women who had 29.5 ±1 day menstrual cycles and found there is an increased propensity for menstruation at or about the full moon.[11]
There is earlier historical evidence of women synchronizing their periods with each other and with the moon. The Temne are the largest ethnic group in Sierra Leone, having been in the current location since at least the 14th century. Largely rural, they live in small villages of about ten households. Even the larger towns have small clan-based enclosures.[12]

… Thomas Buckley studied the Yurok Indians in northwestern California and visited an Indian friend who told him that because his wife was “on her moontime,” she went into seclusion for ten days, cooking and eating her own food by herself.[16] Later, the wife told Buckley that she learned from her aunts and grandmothers that a menstruating woman should isolate herself because this is the time she is at the height of her powers. She was told that in old-time village life, all of the household’s fertile women who were not pregnant menstruated at the same time, a time dictated by the moon. Further, if a woman got out of synchronization with the moon and the other women, she could “get back in by sitting in the moonlight and talking to the moon, asking it to balance [her.]”[17] …
Regarding the use of the moon in restoring menstrual synchrony, Buckley notes recent biological research and findings. The timing of ovulation in humans can be manipulated by exposure to light relatively stronger than that to which subjects are accustomed at a given time of day or night.[18] Buckley describes further research by Dewan, Menkin and Rock[19] which demonstrated that the onset of menstruation itself may be directly affected by the exposure of ovulating women to light during sleep. The researchers found that by exposing ovulating women to the light of a 100-watt bulb during the 14th to 16th nights of their cycles caused the menstrual cycles to become regular, with a significant number of 41 experimental subjects entraining [20] to a 29-day cycle. The three to four nights of exposure was based on the natural duration of full moonlight during the lunar month.

{SEE Lunaception d practice of aligning your cycle to that of the moon, which is believed to increase your chances of conceiving. }

Doing contemporary research on women’s menstrual synchrony with the moon is difficult because of the change in the amount of light exposure we have had in the last hundred years due to the widespread use of electricity. As I read more about this issue, two questions came to mind:  When did human synchrony with the moon first occur and why? The previous studies mentioned here seem to show that women’s menstrual cycles are influenced by a certain amount of light and that pheromones excreted by women can keep them synchronized.

… it appears that Homo was eating far better than Australopithecus. Although many anthropologists believed this was based on meat-eating, there is evidence that regular meat eating began to occur earlier, about 2.5 million years ago. It is hard to explain the long delay before the new species appeared. Wrangham’s theory is that Australopithecus learned to use fire to cook food which improved the digestibility and range of plant foods. He believes that it is also possible that the cooking of meat was highly significant. Thus, the availability of more, digestible food which was cooked shortened the change from Australopithecus into the first human genus, Homo. Why is the cooking of meat important beyond the change in body size and stature? Having cooked food items may have had a profound change on the social and sexual system of early humans.[24] If food items had to be accumulated into a small area and retained there for several minutes or hours to be cooked, larger males would have stolen food from females. Females needed to protect their hard-won food supplies and bonded with certain males to help them protect their food from scroungers. Therefore, females who were more sexually attractive all the time obtained a higher quality of food guardian. To Wrangham, this would explain why early female humans evolved menstrual cycles which allowed sex to occur at any time.

Knight’s model involves a strong bonding of females for it to work. He suggests that women ovulated at full moon and thus menstruated at the dark of the moon. Women had to agree that menstrual bleeding meant no sex. The men therefore used this time to hunt, going away from the women and children and returning with meat. Even though not all women were menstruating because some were pregnant or lactating, all women had to collectively share in the symbolic protection of the menstruants to make sure that all the women would share in the meat. Since the females were capable of mating at any time during the cycle, the advantage for all women to agree to no sex at a particular time allowed for better food resources and at the same time, gave support to pregnant women and young children. The tribe then would have better child survival and as it grew, women could benefit from shared knowledge from mothers and grandmothers.
The men would also have to develop a bond which would not allow anyone to stay behind and have access to the women. It would also be important that women in nearby tribes would be synchronizing their cycles and withdrawing from sex, so that they men would not have access to other women. If the men from other tribes were hunting at the same time, it would benefit them to hunt collectively, which might be needed in order to capture and kill the large herbivores of the Upper Paleolithic time period with primitive weapons. Since men could sometimes be away for long periods, they would have a deadline of bringing home the meat — the full moon, which is when the women would be ovulating. As the meat was brought back, celebration and sexual contact began again. Thus, the full moon celebrations were the foundation for much more than the night sky, they celebrated the return of sexual relations, feasting and the success of the contract.
Judy Grahn argues that men were more interested in the hunt because it drew blood and allowed them to participate in “parallel menstrual rites.”[28] As women created menstrual rituals and seclusion rites, men too had to create rites of their own, centered on the same subject.[29] These “parallel menstruation rites” involve bloodletting and even visionary or hallucinatory states. According to Grahn, the point of the men’s rites, which include the hunt, especially for creatures with horns in lunar shapes, goes beyond the need for meat to the need for the power the men envisioned menstrual blood to have. After all, women were connected to the moon, the waxing and waning of the night light; their blood was considered analogous to such forces as water, “a moving force capable of causing chaos or death.”[30]
To share in the power of the menstruating woman, according to Grahn, men used hunting seclusions similar to the menstrual seclusions to entrain with the light, water and other elements of the natural world. The connection with the blood of the animals they killed may have also have brought them the power they sought.
Craig Stanford, although not writing about menstruation but about meat-eating and human evolution, supports the idea that in all human societies from forager to pastoralist to farmer, meat is a highly valued food resource, accorded a status far beyond its nutritional worth.[31] He believes that the role of meat in human society has never been merely nutritional, and compares humans to chimpanzees, who use meat to secure and maintain political alliances, to publicly snub rivals, and at times to attract estrous females.
During the time of human cultural development, I believe, in concert with Grahn and Knight, the moon continued to be a signal for women to bond together, menstruate at the same time and to develop art, music, dance and ritual. Men too, then, learned to live by the phases of the moon, developing their own rituals, and seeking the power they saw in the female form and blood.

{SEE ALSO The Full Moon’s Pull on Fertility: How Lunaception can Affect a Woman’s Menstrual Cycle}

Read more at Suite101: The Full Moon’s Pull on Fertility: How Lunaception can Affect a Woman’s Menstrual Cycle |

Atmoko, Suci Utami and Jan A.R.A.M. Van Hooff. “Alternative Male Reproductive Strategies: Male Bimaturism in Orangutans.” Sexual Selection in Primates: New and Comparative Perspectives. Ed. Peter M. Kappeler and Carel P. van Schaik. Cambridge: Cambridge University Press, 2004.
Cutler, Winnifred B., Wolfgang M. Schleidt, Erika Freidmann, George Preti, and Robert Stine. “Lunar Influences on The Reproductive Cycle in women,” Human Biology 59 (1987) <>
Birnbaum, Lucia Chiavola. Dark Mother: African Origins and Godmothers. Lincoln, NE: Authors Choice Press, 2001.
Buckley, Thomas. “Menstruation and the Power of Yurok Women.” Blood Magic: The Anthropology of Menstruation. Ed. Thomas Buckley and Alma Gottlieb. Berkeley and Los Angeles: University of California Press, 1988.
Dewan, E. M, M.F. Menkin, and J. Rock. “Effect of Photic Stimulation on the Human Menstrual Cycle.” Photochemistry and Photobiology 28 (1978):     581-585.
Galdikas, Birute M.F. “Orangutan Reproduction in the Wild.” Reproductive Biology of the Great Apes: Comparative and Biomedical Perspectives. Ed.   Charles Graham. New York:  Academic Press, 1981.
Grahn, Judy. Blood, Bread and Roses: How Menstruation Created the World. Boston:  Beacon Press, 1993.
Kaplan, Gisela and Lesley J. Rogers. The Orangutans. Cambridge: Perseus Publishing, 2000.
Knight, Chris. Blood Relations: Menstruation and the Origins of Culture. New Haven:  Yale University Press, 1991.
Lamp, Frederick. “Heavenly Bodies: Menses, Moon, and Rituals of License among the Temne of Sierra Leone.” Blood Magic: The Anthropology of Menstruation.  Ed. Thomas Buckley and Alma Gottlieb. Berkeley and Los          Angeles:  University of California Press, 1988
McClintock, Martha. “Menstrual Synchrony and Suppression.” Nature 229 (1973): 244-5.
____. “Regulation of Human Pheromones.” Nature 392 (1998): 177-179.
Menaker, Walter and Abraham Menaker. “Lunar Periodicity in Human        Reproduction:  A Likely Unit of Biological Time.”  American Journal of      Obstetrics and Gynecology 117 (1973):  413.
Rodman, Peter S. and John C. Mitani. “Orangutans: Sexual Dimorphism in a Solitary Species.” Primate Societies. Ed. Barbara B. Smuts, Dorothy L. Cheney, Robert M. Seyfarth, Richard W. Wrangham, Thomas T. Struhsaker. Chicago: The University of Chicago Press, 1987
Schnayerson, Michael. “The Map of Us All.” National Geographic Adventure. August 2005: 78+.
Shepherd, Janet E. “Your Menstrual Period; As Unique as You Are.” Vibrant Life. Internet. March-April, 1990.
Shuttle, Penelope and Peter Redgrove. The Wise Wound: The Myths, Realities, and Meanings of Menstruation. New York: Grove Press, 1986.
Stanford, Craig B. “The Ape’s Gift:  Meat-eating, Meat-sharing, and Human Evolution.” Tree of Origin: What Primate Behavior Can Tell Us About Human Social Evolution. Ed. Frans B. M. de Waal. Cambridge: Harvard University Press, 2001. 95-118.
Wrangham, Richard W. “Out of the Pan, Into the Fire:  How Our Ancestors’ Evolution Depended on What They Ate.” Tree of Origin: What Primate Behavior Can Tell Us About Human Social Evolution. Ed. Frans B. M. de    Waal. Cambridge:  Harvard University Press, 2001. 119-144.

[1] J Grahn, Blood, Bread and Roses, (Boston:  Beacon Press, 1993).

[2] Metaformic theory is the basis for Grahn’s book which describes metaforms, the act or form of instruction that makes a connection between menstruation and a mental principle (20). Grahn uses rituals, myths, patterns, words, art, body ornament and even food to show how menstruation is at the heart of human culture.

[3]  Birute M.F. Galdikas, “Orangutan Reproduction in the Wild,” Reproductive Biology of the Great Apes:  Comparative and Biomedical Perspectives, ed. Thomas Buckley and Alma Gottlieb (Berkeley and Los Angeles:  University of California Press, 1988), 284.

[4]  Janet E. Shepherd, “Your Menstrual Period,” Vibrant Life, March-April 1990,

[5] Penelope Shuttle and Peter Redgrove, The Wise Wound:  The Myths, Realities and Meanings of Menstruation (New York:  Grove Press, 1986), 149. Also Winnifred B. Cutler et al., “Lunar Influences on the Reproductive Cycle in Women,” Human Biology 59 (1987),

[6] Walter Menaker and Abraham Menaker, “Lunar Periodicity in Human Reproduction:  A Likely Unit of Biological Time,” American Journal of Obstetrics and Gynecology 117 (1973), 413, quoted in Shuttle and Redgrove, 149-150.

[7] Arne Sollberger in his book, Biological Rhythm Research (Amsterdam: Elsevier, 1965) defines the sidereal month of 27.5 days as the period when the moon returns to the same position among the stars and the synodic lunar month of 29.5 days as the time when the moon returns to line up with the sun. Thus, the synodic lunar month is considered the time from new moon to new moon.

[8] In Shuttle and Redgrove, 150.

[9] Martha McClintock, “Menstrual Synchrony and Suppression,” Nature 229 (1973), 244-45.

[10] Martha McClintock, “Regulation of Human Pheromones,” Nature 392 (1998), 177-79.

[11] Cutler, <>

[12] Frederick Lamp, “Heavenly Bodies:  Menses, Moon, and Rituals of License among the Temne of Sierra Leone,” in Blood Magic:  The Anthropology of Menstruation, ed. Thomas Buckley and Alma Gottlieb (Berkeley and Los Angeles:  University of California Press, 1988), 212.

[13] Ibid., 218.

[14] The original source of this quote is from Christian F. Schlenker, A Collection of Temne traditions, fables and proverbs (London: Christian Missionary Society, 1861).

[15] Lamp, 222.

[16] Thomas Buckley, “Menstruation and the Power of Yurok Women,” Blood Magic:  The Anthropology of Menstruation, ed. Thomas Buckley and Alma Gottlieb (Berkeley and Los Angeles:  University of California Press, 1988), 189-190.

[17] Ibid., 191, quoting an unidentified Yurok woman.

[18] Ibid., 189-190.

[19] E.M. Dewan, M.F. Menkin and J. Rock, “Effect of Photic Stimulation on the Human Menstrual Cycle,” Photochemistry and Photobiology 28 (1978), 581-585.

[20] Entrainment is the quality of two similarly timed beats to link up and become synchronized in each other’s presence.

[21] Richard W. Wrangham, “Out of the Pan, Into the fire:  How Our Ancestors’ Evolution Depended on What They Ate,” Tree of Origin: What Primate Behavior Can Tell Us About Human Social Evolution, ed. Frans B.M. de Waal (Cambridge:  Harvard University Press, 2001), 121.

[22] Ibid., 123.

[23] Although A. habilis was first called Homo habilis, some anthropologists have argued that the fossils are closer to Australipithecus than Homo.

[24] Wrangham, 138.

[25] Knight, Blood Relations (New Haven:  Yale University Press, 1991), 169.

[26] Ibid., 199.

[27] Ibid., 270 and also Lucia Chiavola Birnbaum, Dark Mother:  African Origins and Godmothers (Lincoln, NE:  Authors Choice Press, 2001), 5.  National Geographic is currently funding the establishment of eleven DNA-sampling centers around the world to collect 100,000 cheek swabs from indigenous peoples. The goal of the project, led by population geneticist Spencer Wells, is to trace the story of how humankind traveled from our origins in sub-Saharan Africa to populate the planet. This data collected over the next five years may give new insight and understanding to human migration and relationships. Michael Schnayerson, “The Map of Us All,” National Geographic Adventure (August 2005), 78-83, 89-90.

[28] Grahn, 132.

[29] Ibid, 44.

[30] Ibid., 25

[31] Craig B. Stanford, “The Ape’s Gift: Meat-eating, Meat-sharing, and Human Evolution,” Tree of Origin: What Primate Behavior Can Tell Us About Human Social Evolution,” ed. Frans B.M. de Waal (Cambridge:  Harvard University Press, 2001) 109.

[32] Gisela Kaplan and Lesley J. Rogers, The Orangutans (Cambridge:  Perseus Publishing, 2000), 115.

[33] Ibid., 120.

[34] Galdikas, 283.

[35] Peter S. Rodman and John C. Matani, “Orangutans: Sexual Dimorphism in a Solitary Species,” Primate Societies, ed. Barbara B. Smuts et al. (Chicago: University of Chicago Press, 1987), 147.

[36] Each morph is a form or shape that is distinct from the other.

[37] Suci Utami Atmoko and Jan A.R.A.M. Van Hooff, “Alternate Male Reproductive Strategies:  Male Bimaturism in Orangutans,” Sexual Selection in Primates: New and Comparative Perspectives, ed. Peter M. Kappeler and Carel P. van Schaik (Cambridge:  Cambridge University Press, 2004), 203.

[38] Kaplan and Rogers, 119.

Copyright © 2005 Tina Proctor. All rights reserved.